634 research outputs found
First Assessment of Mountains on Northwestern Ellesmere Island, Nunavut, as Potential Astronomical Observing Sites
Ellesmere Island, at the most northerly tip of Canada, possesses the highest
mountain peaks within 10 degrees of the pole. The highest is 2616 m, with many
summits over 1000 m, high enough to place them above a stable low-elevation
thermal inversion that persists through winter darkness. Our group has studied
four mountains along the northwestern coast which have the additional benefit
of smooth onshore airflow from the ice-locked Arctic Ocean. We deployed small
robotic site testing stations at three sites, the highest of which is over 1600
m and within 8 degrees of the pole. Basic weather and sky clarity data for over
three years beginning in 2006 are presented here, and compared with available
nearby sea-level data and one manned mid-elevation site. Our results point to
coastal mountain sites experiencing good weather: low median wind speed, high
clear-sky fraction and the expectation of excellent seeing. Some practical
aspects of access to these remote locations and operation and maintenance of
equipment there are also discussed.Comment: 21 pages, 2 tables, 15 figures; accepted for publication in PAS
Thermal Phase Variations of WASP-12b: Defying Predictions
[Abridged] We report Warm Spitzer full-orbit phase observations of WASP-12b
at 3.6 and 4.5 micron. We are able to measure the transit depths, eclipse
depths, thermal and ellipsoidal phase variations at both wavelengths. The large
amplitude phase variations, combined with the planet's previously-measured
day-side spectral energy distribution, is indicative of non-zero Bond albedo
and very poor day-night heat redistribution. The transit depths in the
mid-infrared indicate that the atmospheric opacity is greater at 3.6 than at
4.5 micron, in disagreement with model predictions, irrespective of C/O ratio.
The secondary eclipse depths are consistent with previous studies. We do not
detect ellipsoidal variations at 3.6 micron, but our parameter uncertainties
-estimated via prayer-bead Monte Carlo- keep this non-detection consistent with
model predictions. At 4.5 micron, on the other hand, we detect ellipsoidal
variations that are much stronger than predicted. If interpreted as a geometric
effect due to the planet's elongated shape, these variations imply a 3:2 ratio
for the planet's longest:shortest axes and a relatively bright day-night
terminator. If we instead presume that the 4.5 micron ellipsoidal variations
are due to uncorrected systematic noise and we fix the amplitude of the
variations to zero, the best fit 4.5 micron transit depth becomes commensurate
with the 3.6 micron depth, within the uncertainties. The relative transit
depths are then consistent with a Solar composition and short scale height at
the terminator. Assuming zero ellipsoidal variations also yields a much deeper
4.5 micron eclipse depth, consistent with a Solar composition and modest
temperature inversion. We suggest future observations that could distinguish
between these two scenarios.Comment: 19 pages, 10 figures, ApJ in press. Improved discussion of gravity
brightenin
z'-band Ground-Based Detection of the Secondary Eclipse of WASP-19b
We present the ground-based detection of the secondary eclipse of the
transiting exoplanet WASP-19b. The observations were made in the Sloan z'-band
using the ULTRACAM triple-beam CCD camera mounted on the NTT. The measurement
shows a 0.088\pm0.019% eclipse depth, matching previous predictions based on H-
and K-band measurements. We discuss in detail our approach to the removal of
errors arising due to systematics in the data set, in addition to fitting a
model transit to our data. This fit returns an eclipse centre, T0, of
2455578.7676 HJD, consistent with a circular orbit. Our measurement of the
secondary eclipse depth is also compared to model atmospheres of WASP-19b, and
is found to be consistent with previous measurements at longer wavelengths for
the model atmospheres we investigated.Comment: 20 pages, 10 figures. Published in the ApJ Supplement serie
The continuous period search method and its application to the young solar analogue HD 116956
We formulate an improved time series analysis method for the analysis of
photometry of active stars. This new Continuous Period Search (CPS) method is
applied to 12 years of V band photometry of the young solar analogue HD 116956
(NQ UMa). The new method is developed from the previous Three Stage Period
Analysis (TSPA) method. Our improvements are the use of a sliding window in
choosing the modelled datasets, a criterion applied to select the best model
for each dataset and the computation of the time scale of change of the light
curve. We test the performance of CPS with simulated and real data. The CPS has
a much improved time resolution which allows us to better investigate fast
evolution of stellar light curves. We can also separate between the cases when
the data is best described by periodic and aperiodic (e.g. constant brightness)
models. We find, however, that the performance of the CPS has certain
limitations. It does not determine the correct model complexity in all cases,
especially when the underlying light curve is constant and the number of
observations too small. Also the sensitivity in detecting two close light curve
minima is limited and it has a certain amount of intrinsic instability in its
period estimation. Using the CPS, we find persistent active longitudes in the
star HD 116956 and a "flip-flop" event that occurred during the year 1999.
Assuming that the surface differential rotation of the star causes observable
period variations in the stellar light curve, we determine the differential
rotation coefficient to be |k|>0.11. The mean timescale of change of the light
curve during the whole 12 year observing period was T_C=44.1 d, which is of the
same order as the predicted convective turnover time of the star. We also
investigate the presence of activity cycles on the star, but do not find any
conclusive evidence supporting them.Comment: 14 pages, 11 figures, 3 table
Influence of Containment on the Growth of Germanium-Silicon in Microgravity
This investigation involves the comparison of results achieved from three types of crystal growth of germanium and germanium-silicon alloys: Float zone growth, Bridgman growth, and Detached Bridgman growth. The fundamental goal of the proposed research is to determine the influence of containment on the processing-induced defects and impurity incorporation in germanium-silicon (GeSi) crystals (silicon concentration in the solid up to 5%) for three different growth configurations in order to quantitatively assess the improvements of crystal quality possible by detached growth
Making the invisible enemy visible.
Structural biology plays a crucial role in the fight against COVID-19, permitting us to ‘see’ and understand SARS-CoV-2. However, the macromolecular structures of SARS-CoV-2 proteins that were solved with great speed and urgency can contain errors that may hinder drug design. The Coronavirus Structural Task Force has been working behind the scenes to evaluate and improve these structures, making the results freely available at https://insidecorona.net/
"It's making contacts" : notions of social capital and implications for widening access to medical education
Acknowledgements Our thanks to the Medical Schools Council (MSC) of the UK for funding Study A; REACH Scotland for funding Study B; and Queen Mary University of London, and to the medical school applicants and students who gave their time to be interviewed. Our thanks also to Dr Sean Zhou and Dr Sally Curtis, and Manjul Medhi, for their help with data collection for studies A and B respectively. Our thanks also to Dr Lara Varpio, Uniformed Services University of the USA, for her advice and guidance on collating data sets and her comments on the draft manuscript.Peer reviewedPublisher PD
Venus transit 2004: Illustrating the capability of exoplanet transmission spectroscopy
The transit of Venus in 2004 offered the rare possibility to remotely sense a
well-known planetary atmosphere using ground-based observations for absorption
spectroscopy. Transmission spectra of Venus' atmosphere were obtained in the
near infrared using the Vacuum Tower Telescope (VTT) in Tenerife. Since the
instrument was designed to measure the very bright photosphere of the Sun,
extracting Venus' atmosphere was challenging. CO_2 absorption lines could be
identified in the upper Venus atmosphere. Moreover, the relative abundance of
the three most abundant CO_2 isotopologues could be determined. The
observations resolved Venus' limb, showing Doppler-shifted absorption lines
that are probably caused by high-altitude winds.
This paper illustrates the ability of ground-based measurements to examine
atmospheric constituents of a terrestrial planet atmosphere which might be
applied in future to terrestrial extrasolar planets.Comment: 7 pages, 5 figures, 1 tabl
A near-infrared interferometric survey of debris disk stars. I. Probing the hot dust content around epsilon Eridani and tau Ceti with CHARA/FLUOR
We probed the first 3AU around tau Ceti and epsilon Eridani with the CHARA
array (Mt Wilson, USA) in order to gauge the 2micron excess flux emanating from
possible hot dust grains in the debris disks and to also resolve the stellar
photospheres. High precision visibility amplitude measurements were performed
with the FLUOR single mode fiber instrument and telescope pairs on baselines
ranging from 22 to 241m of projected length. The short baseline observations
allow us to disentangle the contribution of an extended structure from the
photospheric emission, while the long baselines constrain the stellar diameter.
We have detected a resolved emission around tau Cet, corresponding to a
spatially integrated, fractional excess flux of 0.98 +/- 0.21 x 10^{-2} with
respect to the photospheric flux in the K'-band. Around eps Eri, our
measurements can exclude a fractional excess of greater than 0.6x10^{-2}
(3sigma). We interpret the photometric excess around tau Cet as a possible
signature of hot grains in the inner debris disk and demonstrate that a faint,
physical or background, companion can be safely excluded. In addition, we
measured both stellar angular diameters with an unprecedented accuracy:
Theta_LD(tau Cet)= 2.015 +/- 0.011 mas and Theta_LD(eps Eri)=2.126 +/- 0.014
mas.Comment: 8 pages, 5 figures, to appear in Astronomy and Astrophysic
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